Cellophane coating having improved wet stretch at low temperatures



CELLOPHANE COATING HAVING IMPROVED WET STRETCH AT LOW TEMPERATURES William 0. Brillhart, LeRoy Gallant, and James N. Carver, Fredericksburg, Va., assignors to American Viscose Corporation, Philadelphia, -Pa., a corporation of Delaware No Drawing. Filed Aug. 12, 1957, Ser. No. 677,791 Claims. or. 117-144) This invention is directed to an improved cellophane coating. More specifically it is directed to an improved plasticizer for the conventional nitrocellulose coatings used on cellophane.

A substantial amount of cellophane production is used in packaging fresh red meat for super-market display. The cellophane intended for this purpose is coated only on one side and when it is wrapped on meat the cellophane is stretched tight and sealed in place. When the meat juices wet the inner surface of the wrapper they cause it to swell. If the cellophane coating does not have a high degree of stretch it will crack and split and the meat will blacken and discolor in those areas as a result of dehydration. The nitrocellulose coatings usually employed on cellophane do not always have the desired degree of wet stretch required for this purpose. Hence the object of this invention is to provide an improved cellophane coating having a high wet stretch at temperatures in the range of0-5 0., since red meat is usually stored under these conditions.

We have found that acetyl tributyl citrate, when used as the major component of the plasticizer for 'a conven- States Patent 6 in ice water for one hour and stretching the film in a transverse direction, it was observed that the base film ruptured at about 90-110% elongation without prior rupture of the coating, whereas coatings prepared with only 6-8 parts of liquid plasticizer ruptured under the same test at 40-50% elongation without rupture of the base film.

Meat packaging tests. confirmed .the high degree of protection. afforded by this coating in resisting rupture due to expansion when rewet by meat juices. They also I revealed a high degree of resistance to handling, squeezing, and tumbling such as would be experienced in regular display of the meat packages in. a commercial market.

The following proportions give a fair indication of the range of the various components of lacquer, in parts by weight of the total, exclusive of solvent:

Percent Nitrocellulose 4 5-55 Total plasticizers 36-44 Resin 0-12 Parafiin 3-6 Bentonite V 51-3 Based onlacquer solids the acetyl tributyl citrate may tional nitrocellulose coating, will produce lacquers having 1 a high degree of wet stretch at low temperatures. Acetyl tributyl citrate is a water White, high boiling liquid which is soluble in most common organic solvents. It is insoluble in water and resistant tohydrolysis. Toxicity studieshave shown this ester may tially non-toxic. It is compatible with most natural and synthetic resins. The use of acetyl tributyl citrate as a nitrocellulose plasticizer per se is described at some length in an article entitled Citric Acid Ester Plasticizers, by Prescott and Cragwell, Modern Plastics, October 1952, page 134. However, so far as known this ester has not been employed in a nitrocellulose coating especially designed for use on a cellophane wrapper which requires a high wet stretch at low temperatures.

A typical formula for a nitrocellulose coating composition is as follows:

Parts Nitrocellulose 50 Acetyl tributyl citrate (liquid plasticizer) 26 Dicyclohexyl phthalate (solid plasticizer) 13 Alkyd resin 5 Paraflin 4 Bentonite 2 A 10 gallon batch of nitrocellulose lacquer was prepared using the proportions recited above. An 18-inch wide roll of cellophane was given an anchor coating of be considered essenvary from 15-44% by Weight, i.e., it may constitutethe entire plasticizer since there is nov blocking problem here because one does not stick two coated sides together; The preferred proportion forthe acetyl tributyl citrate is 20-34% by weight of the lacqner solute .gFor fresh meatwrapping theliquidplasticizer should be at least /2 the total plasticizer content in orderto give sufficient wet strength. The preferred solid plasticizers for use with the citrate include Sylflex (phthalimidoethyl propionate), dicyclohexyl phthalate, and ethyl benzoyl benzoate. Preferred resins are ester gum, copal, dammar, and maleic-modified rosin esters.

The various components described above are to be considered simply as illustrative but not limiting as to the components which could be used in the nitrocellulose lacquer. The solid plasticizers which could be used with the acetyl tributyl citrate include diphenyl phthalate, ethylene glycol dibenzoate, N-ethyl p-toluene sulfonamide, cyclohexyl p-toluene sulfonamide, ethyl oxanilate, di-

isobutyl tartrate, sucrose octo-acetate, acetanilide, phenyl benzoate, naphthyl benzoate, glyceryl benzoate, triphenyl phosphate, camphor, etc.

Other resins in addition to those specified above would include resinates, hydrogenated rosin, hydrogenated rosin esters, kauri, alkyd resins, vinyl derivatives, chlorinated diphenyl resins, and soluble resins of the phenol-formaldehyde type.

The wax or wax-like material used in moistureproofing as moistureproofing agents include, in addition to parafiin, petrolatum, ceresin, japan wax, palm wax, beeswax, certain chlorinated hydrocarbons, Chinese insect wax, or other synthetic waxes or wax-like materials may be used. If some of these waxes are too soft for the purpose desired, they may be mixed with harder waxes of the group or with carnauba wax, candelilla wax or other harder waxes. Generally, paraffin serves as a satisfactory moistureproofing agent which may be hardened, if necessary, by admixture with carnauba wax or candelilla wax.

Anchor coatings are well known and a variety of these could be used in the present application. These would include phenol formaldehyde resins, urea formaldehyde resins, melamine formaldehyde resins,.polyethylene imine having a degree of polymerization above 50, etc.

Instead of the bentonite slip agent one may use talc, kaolinite, ZnO, etc.

As solvents, there may be employed any of the known "lacquer solvents such as alcohols, 'k et'ones, esters, hydrocarbons, ethers, halogenated hydrocarbons, nitro paraflins, or mixtures of the foregoing solvents, etc. 7

ApplicationfSe'rial No. 677,802, filed August '12, 1957, wherein Brillhart is a co-applicant, discloses and claims 'the use of acetyl tributyl citrate in a nitrocellulose coating on cellophane in order to prevent ink-bleeding thereon.

We claim:

l. A sheet of regenerated cellulose carrying a coating havinga high wet stretch at temperatures in the range of about to C., said coating comprising as its principal constituents nitrocellulose and a plasticizer composition, said plasticizer composition consisting essentially of about 36 to 44% by weight of said coating, acetyl tributyl citrate constituting one component of'said plas ticizer composition and being present in an amount of from about '15 to 44% by weight of said coating, the balance of said plasticizer composition being a solid plasticizer selected from the group consisting of phthalimidoethyl propionate, dicyclohexyl phthalate, ethyl benzoyl benzoate, diphenyl phthalate, ethylene glycol dibenzoate, N-ethyl p-toluene sulfonamide, cyclohexyl ptoluene sulfonamide, ethyl oxanilate, diisobutyl tartrate, sucrose octo-acetate, acetanili-de, phenyl benzoate, naphthyl benzoate, glyceryl benzoate, triphenyl phosphate, and camphor.

2. The coated sheet of claim 1 wherein said acetyl tributyl citrate varies from about 20 to 34% by weight of said coating and said solid plasticizer varies from about 2 to 24% by weight of said coating.

3. The sheet of claim '2 wherein said solid plasticizer is phthalimidoethyl propionate.

4. The sheet of claim 2 wherein said solid plasticizer is dicyclohexyl phthalate.

5. The sheet of claim 2 wherein said solid plasticizer is ethyl benzoyl benzoate,.

6. A method of preparing a sheet of regenerated cellulose having a coating which possesses a high wet stretch at temperatures in the range between about 0 and 5 C. comprising applying to said sheet of regenerated cellulose a lacquer containing as its principal constituents nitrocellulose and acetyl tributyl citrate as a liquid plasticizer, said lacquer exclusive of the solvent therefor comprising in percent by Weight about 45 to about nitrocellulose and about 36 to about 44% by weight of plasticizer, of which about 15 to 44% by weight is acetyl tributyl citrate and the balance of said plasticizer being a solid plasticizer selected from the group consisting of phthalimidoethyl propionate, dicyclohexyl phthalate, ethyl benzoyl benzoate, diphenyl phthalate, ethylene glycol dibenzoate, N-ethyl p-toluene sulfonamide, cyclohexyl p-toluene sulfonarnide, ethyl oxanilate, diisobutyl tartrate, sucrose octo-acetate, acetanilide, phenyl benzoate, naphthyl benzoate, glyceryl benzoate, triphenyl phosphate, and camphor.

7. The method of claim 6 wherein said acetyl tributyl citrate varies from about 20 to about 34% by weight of said lacquer exclusive of solvent therefor and said solid plasticizer varies from about 2 to 24% by weight of said lacquer exclusive of solvent therefor.

8. The method of claim 7 wherein said solidplasticizer is phthalimidoethyl propionate.

9. The method of claim 7 wherein said solid plasticizer is dicyclohexyl phthalate.

10. The method of claim 7 wherein said solid plasticizer is ethyl benzoyl benzoate.

References Cited in the file of this patent UNITED STATES PATENTS 1,997,105 Cornwell Apr. 9, 1935 2,000,251 Rankin May 7, 1935 2,177,645 Flint et al. Oct. 31, 1939 2,279,788 Iebens Apr. 14, 1942 2,311,831 Heaven et al. Feb. 23, 1943 2,770,555 Cornwell Nov. 13, 1956 FOREIGN PATENTS 753,318 Great Britain July 25, 1956 OTHER REFERENCES Prescott et al.: Modern Plastics, vol. 30, 10/52, p. 134 ff. 

6. A METHOD OF PREPARIN A SHEET OF REGENERATED CELLULOSE HAVING A COATING WHICH POSSESSES A HIGH WET STRETCH AT TEMPERATURES IN THE RANE BETWEEN ABOUT 0 AND 5* C. COMPRISING APPLYING TO SAID SHEET OF REGENERATED CELLULOSE A LACQUER CONTAINING AS ITS PRINCIPAL CONSTITUENTS NITROCELLULOSE AND ACETYL TRIBUTYL CITRATE AS A LIQUID PLASTICIZER, SAID LACQUER EXCLUSIVE OF THE SOLVENT THEREFOR COMPRISING IN PERCENT BY WEIGHT ABOUT 45 TO ABOUT 55% NITROCELLULOSE AND ABOUT 36 TO ABOUT 44% BY WEIGHT OF PLASTICIZER, OF WHICH ABOUT 15 TO 44% BY WEIGHT IS ACETL TRIBUTYL CITRATE AND THE BALANCE OF SAID PLSTICIZER BEING A SOLID PLASTICIZER SELECTED FROM THE GROUP CONSISTING OF PHTHALIMIDOETHYL PROPIONATE, DICYCLOHEXYL PHTHALATE, ETHYL BENZOYL BENZOATE, DIPHENYL PHTHALATE, ETHYLENE GLYCOL DIBENZOATE, N-ETHYL P-TOLUENE SULFONAMIDE, CYCLOHEXYL P-TOLUENE SULFONAMIDE, ETHYL OXIANILATE, DIISOBUTYL TARTRATE, SUCROSE OCTO-ACETATE, ACETANILIDE, PHENYL BENZOATE, NAPHTHYL BENZOATE, GLYCERYL BENZOATE, TRIPHENYL PHOSPHATE, AND CAMPHOR. 